Optical element, method of producing optical elements, coating device, and coating method

ABSTRACT

A method of producing optical elements using a substrate having a recess, which is capable of easily removing a film in the recess, and optical elements formed. The optical element comprises a substrate  1 , an optical waveguide structure layer  10  of resin disposed in a part of the region on the substrate  1 , and a recess  21  formed in the region where the optical waveguide structure layer  10  is not disposed. The optical waveguide structure layer  10  includes an optical waveguide  4  and a clad layer. A coupler layer is disposed between the substrate  1  and the optical waveguide structure layer  10 , and the film thickness distribution range of the coupler layer in the region below the optical waveguide  4  is such that the minimum film thickness is not more than 30 angstroms and the maximum film thickness is not less than 20 angstroms.

TECHNICAL FIELD

This invention relates to a process for producing an optical elementmade of a resin.

BACKGROUND ART

Polyimide type resins attract notice as materials with use of whichoptical elements such as optical waveguides having good opticalcharacteristics can be produced by a simple production process.Polyimide type resins have a high glass transition temperature (Tg) anda superior heat resistance, and hence optical elements produced areexpected to have a long-term reliability, and further, even though theyare made of resins, can withstand soldering. In particular, a polyimidetype resin containing fluorine has characteristic features such that ithas higher light transmission properties and a lower refractive indexthan polyimide type resins containing no fluorine, and hence it issuperior thereto as a material for optical elements.

Such a polyimide type resin containing fluorine, however, has lowadherence to glass, quartz, silicon, silicon oxide, silicon nitride,aluminum, aluminum oxide, aluminum nitride, tantalum oxide, galliumarsenide and so forth which are used as materials for substrates ofoptical elements. Accordingly, an optical-device production method isdisclosed in Japanese Patent Application Laid-open No. H7-174930 inwhich an organozirconium compound layer is formed on a substrate and apolyimide type resin film containing fluorine is formed thereon. Alsodisclosed in Japanese Patent Application Laid-open No. 2000-241640 is astructure in which a film of an organozirconium compound and a resinfilm containing no fluorine are superposingly formed and a polyimidetype resin film containing fluorine is formed thereon.

DISCLOSURE OF THE INVENTION

As stated above, in order to form on a substrate a polyimide type resinfilm containing fluorine which has superior optical characteristics, afilm of an organozirconium compound and a resin film containing nofluorine are conventionally used as bonding layers. These bonding layershave a problem that any too thin layer can not exhibit the action toimprove adherence and on the other hand any too thick layer makes thebonding layer itself brittle.

Meanwhile, as in the case of, e.g., optical elements used in opticalcommunication, in order to facilitate the alignment of optical fiberswith optical elements, the optical elements used to be connected to theoptical fibers can be so structured as to have in each optical element arecess such as a V-groove on which an optical fiber is mounted. Wherespin coating is used to form a bonding layer on a substrate having sucha recess, a bonding layer material solution having accumulated insidethe recess is forced outside by centrifugal force. Hence, depending onthe properties of the bonding layer material solution, a problem mayarise such that the film thickness tends to have a large distribution.Such large distribution of film thickness tends to cause a problem thatthe action to improve adherence can not be attained at the part havingtoo small film thickness and the bonding layer is brittle at the parthaving too large film thickness.

It is an object of the present invention to provide an optical elementhaving an optical-waveguide structure layer made of a resin, and anoptical element having superior adherence between the substrate and theoptical-waveguide structure layer.

To achieve the above object, the present invention provides an opticalelement described below.

The optical element of the present invention comprises a substrate anddisposed thereon an optical-waveguide structure layer made of a resin. Acoupler layer is disposed between the substrate and theoptical-waveguide structure layer. The coupler layer has, in the regionbeneath the optical waveguide embraced in the optical-waveguidestructure layer, a film thickness distribution which is so made as to bein the range of from a minimum film thickness of 30 angstroms or more toa maximum film thickness of 200 angstroms or less.

In this optical element, an organometallic compound layer may be used asthe coupler layer. For example, an organoaluminum compound layer may beused. An organozirconium compound layer may also be used as the couplerlayer, where it may preferably have, in the region beneath the opticalwaveguide, a film thickness distribution in the range of from a minimumfilm thickness of 50 angstroms or more to a maximum film thickness of150 angstroms or less.

In this optical element, the optical-waveguide structure layer may be somade up that it is formed of a resin material containing fluorine and aresin layer containing no fluorine is disposed between the coupler layerand the optical-waveguide structure layer.

The above organozirconium compound layer may also be formed through,e.g., a coating step in which the substrate is disposed in an solventatmosphere, in the state of which the substrate is coated thereon with asolution containing the organozirconium compound and a solvent. Thesolvent constituting the solvent atmosphere may be the same as thesolvent contained in the solution.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing the structure of an optical element100 in First and Second Embodiments of the present invention.

FIG. 2 is a sectional view of the optical element along the line A–A′ inFIG. 1.

FIG. 3 is a sectional view of the optical element along the line B–B′ inFIG. 1.

FIG. 4 is a top view of the optical element shown in FIG. 1.

FIG. 5 is a top view of a wafer-shaped substrate, for describing aprocess for producing optical elements 100 in First and SecondEmbodiments of the present invention.

FIG. 6 is a top view of a wafer-shaped substrate, for describing aprocess for producing optical elements 100 in First and SecondEmbodiments of the present invention.

FIGS. 7( a) to (d) are illustrations showing the steps of cutting thewafer-shaped substrate in the process for producing optical elements 100in First and Second Embodiments of the present invention.

FIGS. 8( a) to (c) are illustrations showing the steps of removing afirst coupler layer 22 and a second coupler layer 23 both in a V-groove21, in the process for producing optical elements 100 in SecondEmbodiment of the present invention.

FIGS. 9( d) and (e) are illustrations showing the steps of removing thefirst coupler layer 22 and the second coupler layer 23 in the V-groove21, in the process for producing optical elements 100 in SecondEmbodiment of the present invention.

FIG. 10 is an illustration showing a structure wherein a spin coaterused in forming the first coupler layer 22 is being rotated, in theprocess for producing optical elements 100 in Second Embodiment of thepresent invention.

FIG. 11 is an illustration showing a structure wherein the spin coatershown in FIG. 10 stands stopped.

FIG. 12 is an illustration showing a structure wherein a spin coaterused in forming the first coupler layer 22 is being rotated, in theprocess for producing optical elements 100 in Second Embodiment of thepresent invention.

FIG. 13 is an illustration showing a structure wherein a spin coater ofa comparative example is being rotated.

FIG. 14 is an illustration showing a structure wherein a spin coater ofa comparative example is being rotated.

FIGS. 15( a) to (c) are illustrations showing the steps of removing afirst coupler layer 22 and a second coupler layer 23 both in a V-groove21, in the process for producing optical elements 100 in FirstEmbodiment of the present invention.

FIG. 16 is a sectional view along the line A–A′ in FIG. 1, of astructure wherein a notch 25 of the optical element is formed in a largedepth of cut.

BEST MODES FOR PRACTICING THE INVENTION

(Fist Embodiment)

First, the structure of an optical element 100 according to a firstembodiment of the present invention is described with reference to FIGS.1 to 4. The optical element 100 has a silicon single-crystal substrate1, and provided thereon a region in which an optical-waveguidemulti-layer member 10 has been mounted on the silicon single-crystalsubstrate 1, a region 20 in which a V-groove 21 has been disposed, and aregion 30 in which an electrode 7 on which a light-emitting element or alight-receiving element is to be mounted. The optical-waveguidemulti-layer member 10 embraces an optical waveguide 4, and the V-groove21 is a groove to which an optical fiber is to be mounted. As to theV-groove 21, its depth and width are so designed that it stands inalignment with the optical waveguide 4 when an optical fiber with apredetermined diameter is mounted. Hence, e.g., the light-emittingelement is mounted on the electrode 7 and the optical fiber is mountedto the V-groove 21, whereby the light emitted from the light-emittingelement can be made to enter the optical waveguide 4 to allow the lightto be propagated therethrough and enter the optical fiber in a highefficiency. Also, where the light-receiving element is mounted on theelectrode 7, the light having come propagated through the optical fibercan be made to enter the optical waveguide 4 in a high efficiency toallow the light to be propagated through the optical waveguide 4 andmake it emergent to the light-receiving element in a good accuracy.

On the top surface of the substrate 1, a silicon dioxide layer 2 isprovided which is to protect the substrate 1 and control refractiveindexes, and the optical-waveguide multi-layer member 10 is mounted onthe silicon dioxide layer 2. The optical-waveguide multi-layer member 10comprises, as shown in FIG. 3, a first coupler layer 22, a secondcoupler layer 23, a lower clad layer 3, the optical waveguide 4, anupper clad layer 5 in which the optical waveguide 4 is buried, and aprotective layer 9, which are multi-layered in this order on the silicondioxide layer 2. The first coupler layer 22 is a coupler layercontaining an organometallic compound, and the second coupler layer 23is a coupler layer containing no organometallic compound. The lower cladlayer 3, the optical waveguide 4 and the upper clad layer 5 are allformed of a polyimide type resin containing fluorine, having superioroptical characteristics. The first coupler layer 22 and the secondcoupler layer 23 are disposed in order to enhance the adherence betweenthe substrate 1 and the lower clad layer 3.

As the organometallic compound constituting the first coupler layer 22,various compounds may be used as described later. In First Embodiment,an organoaluminum compound layer is used as the first coupler layer 22.As the organoaluminum compound, here is used aluminum acetylacetonate.The first coupler layer 22 is so formed that it has, at least in theregion beneath the optical waveguide 4, a film thickness distribution offrom a minimum film thickness of 30 angstroms or more to a maximum filmthickness of 200 angstroms or less.

The second coupler layer 23 is, in First Embodiment, a polyimide typeresin film containing no fluorine. Here, it is a polyimide layer formedusing PIQ (trade name), available from Hitachi Chemical Co., Ltd. It hasa film thickness of about 0.23 μm.

The lower clad layer 3 and the upper clad layer 5 are here each apolyimide film containing fluorine, formed using OPI-N3105 (trade name),available from Hitachi Chemical Co., Ltd. The lower clad layer 3 has afilm thickness of about 6 μm. The upper clad layer 5 has a filmthickness of about 10 μm at its part just above the optical waveguide 4,and about 15 μm at the part other than that. The optical waveguide 4 iscomposed of a polyimide film containing fluorine, formed using OPI-N3305(trade name), available from Hitachi Chemical Co., Ltd. It has a filmthickness of about 6.5 μm. The protective layer 9 is a polyimide filmformed using PIX-6400 (trade name), available from Hitachi Chemical DuPont Microsystems Co., Ltd. It has a film thickness of about 5 μm at itsend part distant from the optical waveguide 4.

In the optical-waveguide multi-layer member 10, a notch 27 is also soformed that it crosses the optical waveguide 4. To this notch 27, afilter such as a wavelength selection filter or a polarized-light filtermay be inserted through which the light propagated through the opticalwaveguide 4 is made to pass. The notch 27 has a notch angle which isperpendicular to the main plane of the substrate 1 as viewed in FIG. 1.It may also have an angle at which it inclines in respect to the mainplane of the substrate 1.

The V-groove 21 is a groove of about 100 μm in depth which has beenformed by subjecting the silicon single-crystal substrate 1 toanisotropic etching, and has substantially a V-shaped cross section. Atthe boundary between the region 20 in which the V-groove 21 has beendisposed and the optical-waveguide multi-layer member 10, a notch 25formed when an end of the optical-waveguide multi-layer member 10 is cutis present as shown in FIGS. 1, 2 and 3. Similarly, a notch 26 is alsopresent at the boundary between the region 30 of the electrode 7 and theoptical-waveguide multi-layer member 10. Incidentally, the notch depthof the notch 25 may preferably be in such an extent that, as shown inFIG. 16, the leading end of an optical fiber does not come into contactwith the inclined part of the V-groove 21 on the region 10 side when theoptical fiber is mounted to the V-groove 21. A registration mark 33 isalso disposed at the bottom of the notch 25, and registration marks 31and 32 on both sides of the electrode 7 in the region 30. Theseregistration marks 31, 32 and 33 are recesses formed by anisotropicetching simultaneously in forming the V-groove 21.

A process for producing optical elements according to this Embodiment isdescribed below with reference to FIG. 5.

Here, a silicon wafer is made ready for use as the substrate 1. Thestructure shown in FIG. 1 is so formed on this substrate 1 as to becrosswise arranged in a large number. In a post step, the structuresformed are cut off by dicing to separate them into individual opticalelements 100. This enables mass production of a large number of opticalelements 100 shown in FIG. 1. Accordingly, film formation and patterningare carried out at a time on the whole wafer-shaped substrate 1.

First, on the whole top surface of the wafer-shaped substrate 1, thesilicon dioxide layer 2 is formed by thermal oxidation or gaseous-phasedeposition. Thereafter, V-grooves 21 are formed in arrangement as shownin FIG. 5, by photolithography and wet etching utilizing anisotropy ofthe silicon single crystal. Here, recesses used as the registrationmarks 31, 32 and 33 shown in FIG. 4 are also previously formed at thesame time the V-grooves 21 are formed.

A metal film is formed on this wafer-shaped substrate 1, followed bypatterning to form each electrode 7 shown in FIG. 1. Thus, as shown inFIG. 5, V-grooves 21 and electrodes 7 are formed in arrangement in alarge number on the wafer-shaped substrate 1. Incidentally, thepatterning of the metal layer is carried out by vacuum deposition or thelike using a resist pattern layer as a mask. When this resist patternlayer is exposed to light, a photomask may be registered using theregistration marks 31, 32 and 33 formed previously at the same time theV-grooves 21 are formed. Thus, electrodes 7 can be obtained which haveaccurately been registered to the V-grooves 21.

Next, on the whole wafer-shaped substrate 1 shown in FIG. 5, the firstcoupler layer 22 is formed by spin coating. First, as a materialsolution for the first coupler layer 22, a solution prepared bydissolving aluminum acetylacetonate in a solvent N-methyl-2-pyrrolidoneis made ready for use. The substrate 1, on which this material solutionhas been dropped, is rotated by means of a commonly available spincoater to form a wet coating of the material solution. Thereafter, thewet coating formed is dried by heating it at 160° C. for about 5 minutesto form the first coupler layer 22. Thus, the first coupler layer 22 canbe formed on the whole surface of the wafer-shaped substrate 1 shown inFIG. 5. The first coupler layer 22 is so formed that, after drying, atleast in the region beneath the optical waveguide 4, the film thicknessdistribution of from a minimum film thickness of 30 angstroms or more toa maximum film thickness of 200 angstroms or less. Of course, the firstcoupler layer 22 may preferably be so formed that it has, not in theregion beneath the optical waveguide 4 only, but in its entirety, thefilm thickness distribution of from a minimum film thickness of 30angstroms or more to a maximum film thickness of 200 angstroms or less.

Next, the second coupler layer 23 and the first coupler layer 22 areremoved from the top surface of the wafer-shaped substrate 1 at its partcorresponding to the regions 20 and 30 where each optical-waveguidemulti-layer member 10 is not disposed in the optical element having beencompleted. On the wafer-shaped substrate 1, optical elements are soproduced as to be crosswise arranged, and hence the part correspondingto the regions 20 and 30 in the top surface of the wafer-shapedsubstrate 1 is, as shown in FIG. 6, beltlike zones on both sides of eachoptical-waveguide multi-layer member 10. Removing the second couplerlayers 23 and first coupler layers 22 from these beltlike zones makes iteasy for the lower clad layers 3 to be separated from the substrate 1 atthese beltlike zones. This makes the second coupler layers 23 and firstcoupler layers 22 removable by peeling them in the form of belts fromthe part corresponding to the regions 20 and 30 in the step describedlater.

Next, the second coupler layer 23 and the first coupler layer 22 areremoved from the top surface of the wafer-shaped substrate 1 at its partcorresponding to the regions 20 and 30 where each optical-waveguidemulti-layer member 10 is not disposed in the optical element having beencompleted. On the wafer-shaped substrate 1, optical elements are soproduced as to be crosswise arranged, and hence the part correspondingto the regions 20 and 30 in the top surface of the wafer-shapedsubstrate 1 is, as shown in FIG. 6, beltlike zones on both sides of eachoptical-waveguide multi-layer member 10. Removing the second couplerlayers 23 and first coupler layers 22 from these beltlike zones makes iteasy for the lower clad layers 3 to be separated form the substrate 1 atthese beltlike zones. This makes the optical-waveguide multi-layermembers 10 removable by peeling them in the form of belts from the partcorresponding to the regions 20 and 30 in the step described later.

A method by which the second coupler layers 23 and first coupler layers22 are removed from the regions 20 and 30 on the substrate 1 isspecifically described.

In order to remove the second coupler layers 23 and first coupler layers22 only from the regions 20 and 30 on the substrate 1, one maycontemplate disposing a resist film with which only the regions wherethe optical-waveguide multi-layer members 10 are disposed are covered,and etching the second coupler layers 23 and first coupler layers 22 onthe regions 20 and 30. However, deep V-grooves 21 of 100 μm in deptheach are present in the regions 20, and hence the light to which theresist is exposed tend to reflect irregularly at inner walls of theV-grooves 21, so that the light can not easily reach the bottoms andends of the V-grooves 21. Hence, where a positive resist with which theportions exposed to light dissolve at the time of development, theresist tends to remain at the bottoms and ends of the V-grooves 21. Ifthe resist remains at the bottoms and ends of the V-grooves 21, thesecond coupler layers 23 and first coupler layers 22 can not be removedat the time of etching. Accordingly, in this Embodiment, a negativeresist is used to remove the second coupler layers 23 and first couplerlayers 22 from the regions 20 where deep V-grooves 21 are present.

First, as shown in FIG. 15( a), a negative resist film 150 is formed onthe whole surface of the wafer-shaped substrate 1 by coating. Here, as afluid negative resist, ZPN-1100 (available from ZEON Corporation) isused, and this is spin-coated, followed by drying at 100° C. to form thenegative resist film 150. Thereafter, the negative resist film 150 isexposed through a photomask by irradiating it by light emitted from amercury lamp. The photomask is so patterned that only the part where theoptical-waveguide multi-layer members 10 are to be formed is irradiatedby light. Thus, only the resist film 150 at its part where theoptical-waveguide multi-layer members 10 are to be formed are exposed tocause photoreaction to change into a resin insoluble in the developingsolution. More specifically, the resist film 150 at the part of theV-grooves 21 is not exposed, and hence the problem does not rise suchthat the light for exposure reflects irregularly at inner walls of theV-grooves 21.

Thereafter, the negative resist film 150 is developed using atetramethylammonium hydroxide (TMAH) 2.38% by weight solution. Upon thisdevelopment, the negative resist film 150 in unexposed areas dissolvesin the developing solution, and only the negative resist film 150 inexposed areas remains. Also, at the same time, the second coupler layers23 also dissolve in the developing solution, and hence the resist film150 is etched away at its part except the resist film 150 in the exposedareas, so that, as shown in FIG. 15( b), the resist film 150 and secondcoupler layers 23 in the interiors of the V-grooves 21 can completely beremoved. Thus, in this Embodiment, the use of the negative resist film150 enables easy removal of the resist film 150 and second couplerlayers 23 in the interiors of the V-grooves 21.

Thereafter, using as an etching mask the resist film 150 having remainedat the part where the optical-waveguide multi-layer members 10 are to beformed, the first coupler layers 22 are removed by wet etching makinguse of hydrofluoric acid or by reactive ion etching [FIG. 15( c)].Finally, the resist film 150 is removed. Thus, the first coupler layers22 and the second coupler layers 23 can be removed from the part of theregions 20 and 30 and the interiors of the V-grooves 21 of thewafer-shaped substrate 1 shown in FIG. 6.

Next, the wafer-shaped substrate 1 is spin-coated with the aboveOPI-N3105 on the whole top surface thereof to form a material solutionwet coating for the lower clad layer 3. Thereafter, the wet coating isheated by means of a dryer at 100° C. for 30 minutes and then at 200° C.for 30 minutes to cause the solvent to evaporate, and subsequentlyheated at 370° C. for 60 minutes to effect curing to form the lower cladlayer 3 in a thickness of 6 μm.

This lower clad layer 3 is spin-coated thereon with the above OPI-N3305to form a material solution wet coating for the optical waveguide 4.Thereafter, the wet coating is heated by means of a dryer at 100° C. for30 minutes and then at 200° C. for 30 minutes to cause the solvent toevaporate, and subsequently heated at 350° C. for 60 minutes to effectcuring to form a polyimide film of 6.5 μm in thickness, serving as theoptical waveguide 4.

Next, this polyimde film is patterned in the shape of optical waveguides4 by photolithography. This is patterned using a resist pattern layer asan etching mask and by reactive ion etching making use of oxygen ions(O₂-RIE). Thus, the optical waveguides 4 can be formed at a time inarrangement in a large number on the substrate 1 as shown in FIG. 6.Thereafter, the resist pattern layer is peeled. Incidentally, when theresist pattern layer is exposed, the photomask is registered usingregistration marks 33 formed previously at the same time the V-grooves21 are formed. This enables formation of optical waveguides 4 registeredaccurately to the V-grooves 21.

Next, spin coating with OPI-N3105 is so carried out as to cover theoptical waveguides 4 and lower clad layers 3 to form a material solutionwet coating for the upper clad layer 5. Thereafter, the wet coating isheated by means of a dryer at 100° C. for 30 minutes and then at 200° C.for 30 minutes to cause the solvent in the material solution wet coatingto evaporate, and heated at 350° C. for 60 minutes to form the polyimidefilm upper clad layer 5.

The upper clad layer 5 is further spin-coated on its top surface withPIX-6400, followed by heating by means of a dryer at 100° C. for 30minutes and then at 200° C. for 30 minutes to cause the solvent toevaporate, and subsequently heating at 350° C. for 60 minutes to formthe polyimide film protective layer 9 having substantially a flat topsurface and having thickness of about 5 μm at the end part distant fromeach optical waveguide 4.

Next, since the layers including the lower clad layer 3 up to theprotective layer 9 are formed in the regions 20 and regions 30 as wellwhich are regions where these layers are unnecessary, these are removedby peeling them. More specifically, as shown in FIG. 6, notches 25 and26 are made by dicing at boundaries between the regions 20 and theoptical-waveguide multi-layer members 10 and at boundaries between theoptical-waveguide multi-layer members 10 and the regions 30,respectively, where the layers including the lower clad layer 3 up tothe protective layer 9 are cut. Here, the depth of cutting by dicing isset to such depth that the substrate 1 is not cut apart. In the previousstep, the first coupler layers 22 and the second coupler layers 23 havebeen removed from the top surface of the substrate 1 in the regions 20and regions 30. Hence, the adherence between the lower clad layer 3 andthe substrate 1 is small in the regions 20 and regions 30. Hence, thelayers including the lower clad layer 3 up to the protective layer 9which are mounted on the regions 20 and regions 30 can be removed withease in the shape of belts from the substrate 1 because the notches 25and 26 have been made. Thus, in the wafer-shaped substrate 1 shown inFIG. 6, the top surface of he substrate 1 stand uncovered in the regions20 and regions 30.

Next, as the wafer-shaped substrate 1 stands as it is, a notch 27 isformed in each optical-waveguide multi-layer member 10 by dicing. Asolder layer having any desired shape is also optionally formed on eachelectrode 7 in the regions 30 uncovered.

Next, the wafer-shaped substrate 1 is cut by dicing as shown in FIGS. 7(a) and (b) to cut out it in the shape of oblong cards. Theoblong-card-shaped substrates 1 are each cut out into individual opticalelements 100 by dicing as shown in FIGS. 7( c) and (d) to complete theoptical elements 100. Incidentally, the procedure of the dicing step isby no means limited to this procedure. The substrate 1 may be cut bydicing crosswise in the step shown in FIG. 7( a) to form the opticalelements 100 as shown in FIG. 7( d).

As having been described above, in this Embodiment, by using as thematerial solution for the first coupler layer 22 the solution preparedby dissolving the organoaluminum compound (aluminum acetylacetonate) inthe solvent (N-methyl-2-pyrrolidone), the wet coating of the firstcoupler layer 22 is thinly formed without any non-uniformity by means ofa spin coater on the substrate 1 on which the deep V-grooves 21 havebeen formed, to form the first coupler layer 22 having, after drying,the film thickness distribution of from a minimum film thickness of 30angstroms or more to a maximum film thickness of 200 angstroms or less.By forming the first coupler layer 22 to have an appropriate filmthickness distribution range in this way, the action to enhance theadherence between the substrate 1 and the lower clad layer 3 in virtueof the first coupler layer 22 can be brought out, and at the same time aphenomenon can be prevented in which the first coupler layer 22 has solarge film thickness that the first coupler layer 22 itself comesbrittle. Thus, optical elements can be produced which can not easilycause film come-off and have optical-waveguide multi-layer members 10having superior optical characteristics and durability.

In addition, in this Embodiment, the negative resist film 150 is usedwhen the first coupler layer 22 and the second coupler layers 23 areremoved, and hence they can be removed with ease from the interiors ofthe V-grooves 21. Therefore, this makes the second coupler layers 23 andfirst coupler layers 22 removable by peeling them in the form of beltsfrom the regions 20 and 30 after the optical-waveguide multi-layermembers 10 have been formed on the whole surface of the wafer-shapedsubstrate 1, and hence the optical elements 100 having V-grooves 21 canbe mass-produced.

Incidentally, in the above embodiment, described is a structure whereinthe first coupler layer 22 and the second coupler layer 23 formed of thepolyimide resin containing no fluorine are disposed in order to enhancethe adherence between the lower clad layer 3 formed of the polyimideresin containing fluorine and the substrate 1. Instead, it is alsopossible to provide a structure that has no second coupler layer 23. Inthe case when the structure has no second coupler layer 23, theadherence between the lower clad layer 3 and the substrate 1 is somewhatlower than the case when it has the second coupler layer 23. However,since in this Embodiment the first coupler layer 22 is so formed as tobe in an appropriate film thickness distribution range, adherence at alevel feasible in practical use can be maintained in virtue of theaction of the first coupler layer 22.

The optical element 100 having been described above has the V-groove 21on which the optical fiber is mounted, and has the registration marks31, 32 and 33 formed simultaneously when the V-groove 21 is formed. Whenthe optical waveguide 4 is formed, the registration mark 33 is used toregister the V-groove 21 and the optical waveguide 4 accurately. Alsowhen the electrode 7 is formed, the registration marks 31 and 32 areused to register the electrode 7 and the V-groove 21 accurately. Alsowhen the light-emitting element or light-receiving element is mounted onthe electrode 7, the registration marks 31 and 32 are used to registerthe optical axis of the light-emitting element or light-receivingelement accurately to the V-groove 21. Thus, the V-groove 21 and theoptical waveguide 4 are kept in accurate alignment in the direction ofthe main plane at the time of point that the optical element 100 hasbeen completed, and the alignment of the V-groove 21 and the opticalwaveguide 4 can be ensured with ease only by mounting to the former theoptical fiber as designed. Also, when the light-emitting element orlight-receiving element is mounted on the electrode 7, the registrationmarks 31 and 32 are used to make registration, whereby thelight-emitting element or light-receiving element can accurately bealigned to the optical waveguide 4 with ease. This enables easy andaccurate alignment of the light-emitting element or light-receivingelement, the optical waveguide 4 and the optical fiber on the V-groove21, and an optical element can be provided which has a high bondingefficiency.

(Second Embodiment)

Next, a process for producing optical elements 100 according to SecondEmbodiment of the present invention is described.

The optical elements 100 according to the second embodiment are eachstructured to have the shape and layer structure shown in FIGS. 1 to 4like those in First Embodiment, but differ from those in FirstEmbodiment in that an organozirconium compound film is used as the firstcoupler layer 22. The method of spin coating in forming the firstcoupler layer 22 also differs from that in First Embodiment. Further, inthe second embodiment, in the step of removing first coupler layers 22and second coupler layers 23 from regions 20 and 30, a positive resistfilm is used, and exposure and development methods are devised so thatthe resist layer and the second coupler layers 23 can completely beremoved.

In this Embodiment, as the organozirconium compound constituting thefirst coupler layer 22, various compounds may be used as describedlater. Here, a zirconium tributoxyacetylacetonate film is used as thefirst coupler layer 22. The first coupler layer 22 may preferably have,at least in the region beneath the optical waveguide 4, a film thicknessdistribution in the range of from a minimum film thickness of 30angstroms or more to a maximum film thickness of 200 angstroms or less,and particularly preferably from a minimum film thickness of 50angstroms or more to a maximum film thickness of 150 angstroms or less.This is because if its film thickness is less than 30 angstroms, theeffect of improving adherence can not well be brought out to make thelower clad layer 3 tend to come off the substrate 1. This is alsobecause if its film thickness is more than 200 angstroms, the film maycome brittle. Also, the range of from a minimum film thickness of 50angstroms or more to a maximum film thickness of 200 angstroms or lesscorresponds substantially to 5 molecular layers or more to 15 molecularlayers or less when expressed in terms of molecular layers (the lap ofmolecules) of the organozirconium compound. Of course, the first couplerlayer 22 may more preferably have, not in the region beneath the opticalwaveguide 4 only, but in its entirety, the film thickness distributionin the range of from a minimum film thickness of 30 angstroms or more toa maximum film thickness of 200 angstroms or less. How to form the filmand how to measure the film thickness are described later in detail.

The second coupler layer 23 is, like that in First Embodiment, apolyimide resin film containing no fluorine, formed using PIQ (tradename), available from Hitachi Chemical Co., Ltd. It has a film thicknessof about 0.23 μm. Materials and film thickness of the lower clad layer3, upper clad layer 5, optical waveguide 4 and protective layer 9 arealso the same as those in First Embodiment.

A process for producing optical elements according to Second Embodimentis described below.

Like First Embodiment, a silicon wafer is made ready for use as thesubstrate 1. On the whole top surface of the substrate 1, a silicondioxide layer 2 is formed by thermal oxidation or gaseous-phasedeposition. Thereafter, V-grooves 21 are formed in arrangement as shownin FIG. 5. Here, the registration marks 31, 32 and 33 shown in FIG. 4are also formed simultaneously. Thereafter, on the substrate 1, eachelectrode 7 as shown in FIG. 1 is formed. Thus, as shown in FIG. 5,V-grooves 21 and electrodes 7 are formed in arrangement in a largenumber on the wafer-shaped substrate 1.

Next, on the whole wafer-shaped substrate 1 shown in FIG. 5, the firstcoupler layer 22 is formed. First, as a material solution for the firstcoupler layer 22, a solution prepared by dissolving zirconiumtributoxyacetylacetonate in butanol to make up a 1% by weight solutionis made ready for use, and the substrate 1 is coated thereon with thissolution by spin coating. This material solution tends to cause filmthickness non-uniformity at the time of spin coating, compared with thefirst coupler layer 22 material solution used in First Embodiment.Accordingly, any of the following first to third spin coating methodsare used as a spin coating method. The first coupler layer 22 can beformed in the film thickness distribution in the range of from 30angstroms or more to 200 angstroms or less whatever method of the firstto third spin coating methods is used.

The first spin coating method is a method making use of a spin coatershown in FIG. 10. The spin coater shown in FIG. 10 has a stationary cup202 and a rotary cup 210 disposed inside the stationary cup 202. Therotary cup 210 has a cup-shaped main body 207, a substrate mount 206disposed inside the main body 207, and a cover 205 with which the mainbody 207 is covered. The cup main body 207 is connected to a rotarydrive 201, and is rotated around an axis 211. The cup main body 207 isalso provided with a substrate suction through-hole 212 whichcommunicates with the substrate mount 206. This suction through-hole 212is connected to an evacuation system (not shown). The cup main body 207is still also provided with a discharge through-hole 213 from which acoating solution is to be discharged. The discharge through-hole 213 isso formed as to extend from a coating solution inlet 213 a toward theaxis 211. Accordingly, a discharge vent 213 b is disposed nearer to theaxis 211 than to the inlet 213 a.

When the spin coating is carried out using the spin coater shown in FIG.10, the wafer-shaped substrate 1 is mounted on the substrate mount 206,and a organozirconium compound solution is dropped on the substrate 1.Thereafter, the cup main body 207 is covered with a cover 205. Thus, theinternal space of the rotary cup 210 comes to be filled with a solventcontained in the solution, to provide a solvent atmosphere. In thisstate, the rotary cup is rotated, whereupon the solution is coated onthe substrate 1 by centrifugal force. Here, the rotary cup is rotatedfor 90 seconds under conditions of from 500 rpm to 2,000 rpm. Duringthis rotation, since the discharge vent 213 b is disposed nearer to theaxis 211 than to the inlet 213 a, the discharge through-hole 213undergoes a preload from the discharge vent 213 b side toward the inlet213 a by centrifugal force, so that the rotary cup 210 comes to standclosed. Thus, the solution and atmosphere in the rotary cup 210 is notdischarged outside. Hence, the inside of the rotary cup 210 is notevacuated, and any stream of atmosphere is not formed. Moreover, thecover 205 facing the substrate 1 is rotated together with the substrate1 at the same speed, and hence the relative speed between the substrate1 and the cover 205 comes to zero, and the relative speed between theatmosphere between the substrate 1 and the cover 205 and the substrate 1also comes to zero. Thus, the atmosphere of the substrate 1 is filledwith the solvent atmosphere during the rotation of the substrate 1, andalso the solvent atmosphere is rotated together with the substrate 1,where any stream of the atmosphere is present. Hence, the wet coating ofthe solution on the substrate 1 little becomes dry.

Thus, the spin coating is carried out using the spin coater shown inFIG. 10, which can prevent the wet coating from drying during therotation, whereby the wet coating of the material solution for the firstcoupler layer 22 can uniformly be formed even on the substrate 1 wherethe deep V-grooves 21 are arranged in a large number as shown in FIG. 5.According to experiments made by the present inventors, the firstcoupler layer 22 formed by this first spin coating method has been foundto have a film thickness distribution in the range of from a minimumfilm thickness of about 60 angstroms to a maximum film thickness ofabout 113 angstroms on one wafer-shaped substrate 1 in the state the wetcoating is brought to a heat-and-drying step described later. The reasonwhy the thickness non-uniformity can be made very small in this way isconsidered to be that, in the case of the spin coater shown in FIG. 10,the stream of atmosphere is little present and the wet coating can noteasily dry during the rotation of the substrate 1, and hence, eventhough the solution having accumulated in the V-grooves 21 has beenblown off outward by centrifugal force to form a thick wet coatingthere, it spreads to the surroundings to become uniform in the coursethe substrate 1 is further rotated as it is. After the rotation has beencompleted, the centrifugal force comes lost, and hence the solutionflows through the discharge through-hole 213 from its inlet 213 a towardits discharge vent 213 b as shown in FIG. 11. Thus, a stream is producedon which the solvent atmosphere is discharged out of the inside of therotary cup 210. Also, once the cover 205 is opened, the solventatmosphere changes off with the air at once. Thus, the wet coating onthe substrate 1, having been uniformly coated, dries at it is, so that acoating film of the material solution for the first coupler layer 22 isformed.

The second spin coating method is a method making use of a spin coatershown in FIG. 12. The spin coater shown in FIG. 12 is so structured thata substrate mount 220 is directly disposed inside a stationary cup 202and the substrate mount 220 is rotated. The stationary cup 202 iscovered with a cover 222 and closed, where the inside of the rotary cup202 is filled with a solvent contained in the solution, and the spincoating is carried out in a solvent atmosphere. In the structure shownin FIG. 12, the cover 222 stands still and hence correspondingly has thesame relative speed as the rotational speed between it and substrate 1being rotated, so that a stream of solvent atmosphere is producedbetween the substrate 1 and the cover 222. Because of this stream, thesolution on the substrate 1 may more dry than that in the first spincoating method. However, in the second spin coating method, a method isemployed in which, after the rotation has been completed, the solventatmosphere is slowly discharged from a discharge vent 221 provided inthe stationary cup 202, over a period of about 10 minutes at a lowdischarge speed of about 2 to 3 liters/min while the flow rate ismeasured with a flowmeter (not shown), and thereafter the cover 222 isopened. By using this method, the drying speed after the stopping ofrotation is controlled. The first coupler layer 22 formed by this secondspin coating method has been found to have a film thickness distributionin the range of from a minimum film thickness of about 54 angstroms to amaximum film thickness of about 140 angstroms on one wafer-shapedsubstrate 1 in the state the wet coating formed by spin coating has beenbrought to a heat-and-drying step described later. This film thicknessdistribution falls within the range of from 50 angstroms or more to 200angstroms or less which is the range of film thickness non-uniformitythat is desirable for improving adherence, and the action to improveadherence sufficiently can be attained.

The third spin coating method is a method making use of the same spincoater shown in FIG. 12 as that in the second spin coating method and inwhich, after the rotation has been completed, solvent atmosphere isdischarged for 10 minutes controlling the discharge flow rate at 2 to 3liters/min like the second spin coating method, but differs from thesecond spin coating method in that a rest time of 2 minutes is providedafter the rotation has been completed and before the discharge isstarted. The solvent atmosphere is not discharged during this rest timeof 2 minutes. By providing the rest time in this way, the uneven filmthickness having resulted during the rotation is leveled to a certainextent. The first coupler layer 22 formed by this third spin coatingmethod has been found to have a film thickness distribution in the rangeof from a minimum film thickness of about 59 angstroms to a maximum filmthickness of about 138 angstroms on one wafer-shaped substrate 1 in thestate the wet coating formed by spin coating has been brought to aheat-and-drying step described later. This film thickness distributionis narrower than the film thickness distribution obtained in the secondspin coating method.

As a comparative example, a wet coating of the material solution for thefirst coupler layer 22 has been formed using a spin coater shown in FIG.13. The spin coater shown in FIG. 13 resembles the above spin coatershown in FIG. 10, but differs from the FIG. 10 spin coater in that adischarge through-hole 230 is disposed on the circumferential side of amain body 207 of a rotary cup 231. In the coater shown in FIG. 13, therotary cup 231 is rotated, whereupon the solution and internalatmosphere are continuously discharged from the discharge through-hole230 toward the outside by centrifugal force. Hence, the inside of therotary cup comes to have a reduced pressure, and can not maintain thesolvent atmosphere to cause drying under reduced pressure, so that thesolution is coated while being dried. For this reason, the filmthickness distribution after the heat-and-drying step has been found notto fall within the range of from 50 angstroms or more to 200 angstromsor less.

As another comparative example, spin coating has been carried out usinga spin coater shown in FIG. 14, which has the same structure as the spincoater shown in FIG. 12, except that it has no cover 222. The spincoater shown in FIG. 14 has the stationary cup 202 set open, and henceno solvent atmosphere is formed. Also, the atmosphere around thesubstrate 1 stands still, and hence an air stream is produced around thesubstrate 1. Hence, the wet coating dries during the rotation, and hencethe wet coating becomes thick at its part where the solution havingaccumulated in the V-grooves 21 has been flowed toward the outerperiphery, and dries as it stands. Hence, the first coupler layer 22having been brought to the heat-and-drying step has been found to have afilm thickness distribution of from a minimum film thickness of about 5angstroms to a maximum film thickness of about 194 angstroms on onewafer-shaped substrate 1, bringing about a large film thicknessnon-uniformity. Hence, the lower clad layer 3 has come off at the partwhere the first coupler layer 22 has a thickness smaller than 30angstroms.

As described above, in this Embodiment, any of the above first, secondand third spin coating methods is used to carry out the coating with thematerial solution for the first coupler layer 22. Thereafter, the wetcoating formed is dried by heating it at 160° C. for about 5 minutes.Thus, the first coupler layer 22 can be formed on the whole surface ofthe wafer-shaped substrate 1 shown in FIG. 5, in the film thicknessdistribution of from 30 angstroms or more to 200 angstroms or less.Incidentally, the temperature and time in the heat-and-drying step offorming the first coupler layer 22 may preferably appropriately be setto be approximately from 160 to 220° C. and from 5 to 10 minutes.

Next, the first coupler layer 22 is coated thereon with PIQ (tradename), available from Hitachi Chemical Co., Ltd., by spin coating toform a wet coating of a material solution for the second coupler layer23 like that in First Embodiment. Thereafter, the wet coating is heatedto make the solvent evaporate, and is further heated to make it cure toform the second coupler layer 23. The conditions for spin coating are socontrolled that the second coupler layer 23 comes to have a thickness of0.23 μm.

Next, the second coupler layer 23 and the first coupler layer 22 areremoved from the top surface of the wafer-shaped substrate 1 at its partcorresponding to the regions 20 and 30 where each optical-waveguidemulti-layer members 10 is not disposed in the optical element havingbeen completed.

A method by which the second coupler layers 23 and first coupler layers22 are removed from the regions 20 and 30 on the substrate 1 isspecifically described.

In Second Embodiment, using a positive resist, a resist film is formedwith which only the regions where the optical-waveguide multi-layermembers 10 are disposed are covered, and the second coupler layers 23and first coupler layers 22 on the regions 20 and 30 are etched.

First, as shown in FIG. 8( a), a positive resist film 50 is formed onthe whole surface of the wafer-shaped substrate 1 by coating. Here, as afluid negative resist, OFPR800 (available from Tokyo Ohka Kogyo Co.,Ltd.) is used, and this is spin-coated, followed by drying at 100° C. toform the resist film 150. Thereafter, the image of a photomask isexposed using a mercury lamp. Since the positive resist has the naturethat its part exposed changes into a compound capable of dissolving in adeveloping solution, the photomask is so patterned that the regions 20and 30 are irradiated by light and the part where the optical-waveguidemulti-layer members 10 are to be formed is not irradiated by light.Thus, only the resist film 50 at the regions 20 and 30 is exposed tocause photoreaction to change into the compound capable of dissolving ina developing solution.

After the exposure, the positive resist film 50 is developed using atetramethylammonium hydroxide (TMAH) 2.38% by weight solution as thedeveloping solution. Upon this development, as shown in FIG. 8( b), theresist film 50 at the regions 20 and 30 dissolves, and the resist film50 remains only at the part where the optical-waveguide multi-layermembers 10 are to be formed. The second coupler layers 23 also dissolveat the time of development, and hence they are wet-etched and areremoved from the regions 20 and 30. Incidentally, in the V-grooves 21 ofthe regions 20, the light reflects irregularly at inner walls of theV-grooves 21 at the time of exposure, and the light can not easily reachthe bottoms and ends of the V-grooves 21. Hence, the resist film 50 andsecond coupler layers 23 remain partly at the bottoms and ends of theV-grooves 21. Accordingly, in this Embodiment, in order to remove theresist film 50 and second coupler layers 23 remaining there, these areagain exposed using the above photomask, and then developed with TMAH.Thus, the resist film 50 and second coupler layers 23 having remained inthe V-grooves 21 can completely be removed as shown in FIG. 8( c). Evenwhen the positive resist film 50 is used, this method enables the secondcoupler layers 23 to be completely removed from the V-grooves 21 throughthe simple step in which exposure and development are repeated.

Thereafter, using as an etching mask the resist film 150 having remainedat the part where the optical-waveguide multi-layer members 10 are to beformed, the first coupler layers 22 are removed by wet etching makinguse of hydrofluoric acid or by reactive ion etching [FIG. 9( d)]. Thefirst coupler layers 22 have a very small film thickness, and hence thelayers inside the V-grooves 21 can also be removed by wet etching orreactive ion etching. Finally, the resist film 50 is removed [FIG. 9(e)]. Thus, the first coupler layers 22 and the second coupler layers 23can be removed from the part of the regions 20 and 30 and the interiorsof the V-grooves 21 of the wafer-shaped substrate 1 shown in FIG. 6.

Thereafter, in the same manner as in First Embodiment, a lower cladlayer 3, optical waveguides 4, an upper clad layer 5 and a protectivelayer 9 are formed on the wafer-shaped substrate 1, and these layers arepeeled off from the part of the regions 20 and 30, followed by dicingfor each optical element 100 to complete optical elements 100.

As having been described above, in the Second Embodiment, by using asthe material solution for the first coupler layer 22 the solutionprepared by dissolving the organozirconium compound (zirconiumtributoxyacetylacetonate) in the solvent (butanol) and using any of thefirst, second and third spin coating methods, the first coupler layer 22is thinly formed without any non-uniformity in spite of the substrate 1on which the deep V-grooves 21 have been formed. Stated specifically,the film thickness distribution range can be achieved which is of from30 angstroms or more to 200 angstroms or less, in particular, from 50angstroms or more to 150 angstroms or less. This is because the first,second and third spin coating methods are methods of carrying out spincoating in the solvent atmosphere and can keep the wet coating fromdrying during the spin coating. Thus, forming the first coupler layer 22thinly and without any non-uniformity enables enhancement of theadherence between the substrate 1 and the lower clad layer 3, andenables production of optical elements which cannot easily cause filmcome-off and have optical-waveguide multi-layer members 10 havingsuperior optical characteristics and durability.

Now, how to measure the film thickness of the first coupler layer 22 isdescribed.

Described first is how to measure the film thickness as a form that isat the stage where the first coupler layer 22 has been formed on thesubstrate 1.

The film thickness may be measured with a non-contact optical thin-filmgauge F40 (hereinafter “F40”), provided by Filmetrics Inc. and makingmeasurement by reflectance spectroscopy. A specific measuring method isshown below.

First, the initial-stage setting of sensor sensitivity is performed. Onthe metal microscope stage of the above F40, a mirror-polished siliconwafer (recommended is an attachment manufactured by Filmetrics Inc.) isset with its polished surface up, and a sensor sensitivity initial-stagesetting button is set. Next, in the state its light source islight-screened, the dark button is set to perform the initial-stagesetting of sensor sensitivity.

Next, the film thickness of the silicon dioxide layer 2 formed on thesubstrate 1 as a subbing layer is measured. As a measuring methodtherefor, the substrate 1 on which the silicon dioxide layer 2 has beenformed is placed on the microscope stage. The refractive index of thesilicon dioxide layer is set on a refractive-index-setting pictureplane, and the silicon dioxide layer is set to the first layer on ameasurement-parameter-setting picture plane, where the measurementbutton is pushed. Thus, the film thickness of the silicon dioxide layer2 is determined. Measuring the film thickness of the silicon dioxidelayer 2 in this measurement is to enhance the precision of the filmthickness measurement of the first coupler layer 22.

Incidentally, as the refractive index of the silicon dioxide layer 2,the following value is set. In respect of wavelength of 330 nm, arefractive index of 1.480 is set; in respect of wavelength of 577 nm, arefractive index of 1.458; in respect of wavelength of 1, 128 nm, arefractive index of 1.448; and in respect of wavelength of 1,362 nm, arefractive index of 1.446.

Next, the film thickness of the first coupler layer 22 organozirconiumcompound layer is measured. Its procedure is the same as that of themeasuring method on the silicon dioxide layer 2, provided that it isnecessary to input, on a measurement parameter picture plane, the filmthickness of the first-layer silicon dioxide layer 2 that has alreadybeen measured, to set the organozirconium compound layer at the secondlayer.

Here, as the refractive index of the organozirconium compound layer, thefollowing value is set. In respect of wavelength of 633 nm, a refractiveindex of 1.613 is set; in respect of wavelength of 830 nm, a refractiveindex of 1.613; and in respect of wavelength of 1,300 nm, a refractiveindex of 1.613.

Next, the substrate on which the first coupler layer 22 (organozirconiumcompound layer) has been formed is set on the microscope and themeasurement button is pushed, thus the film thickness of the firstcoupler layer 22 can be measured.

As a point to which attention be paid, it is the point that themicroscope in the instrument is focused on the surface of the firstcoupler layer 22 at the time of the measurement of the layer 22, andfocused on the surface of the silicon dioxide layer 2 at the time of themeasurement of the layer 2. It is also desirable for the microscope tohave an objective lens of about 10 magnifications. Under this condition,the minimum measurement limit is about 10 angstroms.

Next, how to measure the film thickness of the first coupler layer 22 isdescribed on the basis of the form of the optical element shown in FIG.1.

As procedure of the measurement, first, the polyimide films secondcoupler layer 23, lower clad layer 3, optical waveguide 4, upper cladlayer 5 and protective layer 9 are removed for the most part of these tomake the top surface of the first coupler layer 22 uncovered. Thesepolyimide films are removed by removing their greater part by dryetching and thereafter removing the remaining polyimide films by wetetching. Next, the first coupler layer 22 is removed by dry etching onlyat its partial area to make the top surface of the underlying silicondioxide layer 2 uncovered. Thereafter, the film thickness of the silicondioxide layer 2 and the film thickness of the first coupler layer 22 aremeasured in the same manner as the above, using F40.

The dry etching to remove the polyimide films is carried out by reactiveion etching making use of oxygen ions (O₂-RIE), which are so etched thata polyimide film remains on the first coupler layer 22 in a thickness ofabout 1 to 2 μm. The remaining polyimide film is removed by wet etchingby subjecting it to immersion treatment at room temperature for about 1hour, using a polyimide film solvent N-methyl-2-pyrrolidone orN,N-dimethylacetamide. As the solvent used here, it is preferable toselect a solvent to which the first coupler layer 22 (organozirconiumcompound layer) has resistance.

Next, the substrate 1 is divided by, e.g., breaking it into two or morepieces. Then, only some divided-substrate pieces are subjected to thereactive ion etching making use of oxygen ions (O₂-RIE) to remove thefirst coupler layer 22. Here, the underlying silicon dioxide layer 2 hasa high resistance to dry etching, and hence the film thickness loss ofthe silicon dioxide layer 2 is 0.01 μm or less, and little adverselyaffects the precision of measurement of the silicon dioxide layer 2formed in a thickness of approximately from 5,000 angstroms to 10,000angstroms.

Thereafter, on a divided-substrate piece where the silicon dioxide layer2 stands uncovered, the film thickness of the silicon dioxide layer 2 ismeasured with F40. Using the measurement data obtained, the filmthickness of the first coupler layer is measured on a divided-substratepiece where the first coupler layer 22 remains. The measurement may bemade in the same manner as the above.

In the Second Embodiment, the positive resist film 50 is used when thefirst coupler layers 22 and the second coupler layers 23 are removed,and the exposure and the development are performed a plurality of times,whereby they can relatively easily be removed from the interiors of theV-grooves 21. Therefore, this makes the second coupler layers 23 andfirst coupler layers 22 removable by peeling them in the form of beltsfrom the regions 20 and 30 after the optical-waveguide multi-layermembers 10 have been formed on the whole surface of the wafer-shapedsubstrate 1, and hence the optical elements 100 having V-grooves 21 canbe mass-produced.

In Second Embodiment, the positive resist film 50 is used when the firstcoupler layer 22 and second coupler layer 23 are removed. Instead, it isalso possible of course to use the negative resist film 150 as describedin First Embodiment.

In the above Embodiments, described is a structure wherein the firstcoupler layer 22 and the second coupler layer 23 formed of the polyimideresin containing no fluorine are disposed in order to enhance theadherence between the lower clad layer 3 formed of the polyimide resincontaining fluorine and the substrate 1. Instead, it is also possible toprovide a structure that has no second coupler layer 23. In the casewhen the structure has no second coupler layer 23, the adherence betweenthe lower clad layer 3 and the substrate 1 is somewhat lower than thecase when it has the second coupler layer 23. However, adherence at alevel feasible in practical use can be maintained in virtue of theaction of the first coupler layer 22.

In the First and Second Embodiments, the wet etching is used to removethe second coupler layer 23. If, however, e.g., reactive ion etching(RIE) is used, the anisotropy of plasma is so strong that the shape ofthe second coupler layer 23 at the flat portion of the substrate 1 canbe controlled with ease, but the resin of the second coupler layer 23present inside the V-groove 21 whose slanting surfaces incline obliquelyis removable in a poor efficiency. On the other hand, if ashing is usedto remove the second coupler layer 23, the isotropy of plasma is sostrong that, in an attempt to remove the resin of the second couplerlayer 23 present inside the V-groove 21, the shape of the second couplerlayer 23 at the flat portion of the substrate 1 can be controlled withdifficulty. Also, if the reactive ion etching and the ashing are used incombination to remove the second coupler layer 23 in the flat portion ofthe substrate 1 and in the V-groove 21 by the RIE and the ashing,respectively, side etching tends to take place at the time of ashing, inthe second coupler layer 23 at the part where the optical-waveguidemulti-layer member 10 is to be formed. On the other hand, the use of thewet etching as in this Embodiment enables removal of the second couplerlayer 23 with ease. Also, in this Embodiment, the use of the wet etchant(TMAH) as the developing solution enables simultaneous removal of theresist film 50 and the second coupler layer 23, and hence there can bean advantage that the number of steps can be smaller.

In the optical elements according to First and Second Embodiments havingbeen described above, the optical waveguide 4 has a linear shape. Theoptical waveguide 4 of the optical-waveguide multi-layer member 10 mayhave, without limitation to the linear shape, the shape of a y-branch,an x-type or the like in conformity with functions required as opticalelements. Correspondingly thereto, each optical element may be sostructured as to have a plurality of V-grooves 21 so that a plurality ofoptical fibers can be mounted. In respect of the electrode 7 as well, aplurality of electrodes may be disposed so that a plurality oflight-emitting elements or light-receiving elements can be mounted.

In the present invention, the optical element refers to one in which,using as a substrate an inorganic material such as glass or quartz, asemiconductor or metallic material such as silicon, gallium arsenide,aluminum or titanium, a polymeric material such as polyimide orpolyamide, or a composite material of any of these, an opticalwaveguide, an optical coupler, an optical branching filter, an opticalattenuator, an optical diffraction grating, an optical amplifier, anoptical interference filter, an optical filter, an optical switch, awavelength converter, a light-emitting element, a light-receivingelement or a composite of any of these has been formed on the substrate.On the substrate, a semiconductor device such as a light-emitting diodeor a photodiode may also be formed. Further, in order to protect thesubstrate or control the refractive index, a film of silicon dioxide,silicon nitride, aluminum oxide, aluminum nitride or tantalum oxide mayalso be formed on the substrate.

In First Embodiment, the first coupler layer 22 is formed of anorganoaluminum compound. In Second Embodiment, the second coupler layer23 is formed of an organozirconium compound. Instead, the first couplerlayer 22 may be so formed as to contain at least one of anorganoaluminum compound and an organozirconium compound.

The organozirconium compound constituting the first coupler layer 22 inSecond Embodiment may preferably be a zirconium ester or a zirconiumchelate compound.

The zirconium ester may include tetrapropyl zirconate and tetrabutylzirconate. The zirconium chelate compound may includetetrakis(acetylacetonato)zirconium,monobutoxytris(acetylacetonato)zirconium,dibutoxybis(acetylacetonato)zirconium,tributoxyacetylacetonatozirconium, tetra(ethylacetylacetonato)zirconium,monobutoxytris(ethylacetylacetonato)zirconium,dibutoxybis(ethylacetylacetonato)zirconium,tributoxyethylacetylacetonatozirconium,tetrakis(ethyllactonato)zirconium,bis(bisacetylacetonato)bis(ethylacetylacetonato)-zirconium,monoacetylacetylacetonatotris-(ethylacetylacetonato)zirconium andmonobutoxymonoacetylacetonatobis(ethylacetyl-acetonato) zirconium. Ineither case of the zirconium ester and the zirconium chelate compound,examples are by no means limited to these as long as they are thosecontaining zirconium oxide at the time of film formation. Any of theabove compounds may be used alone or in the form of a mixture.

The organozirconium compound is dissolved in an organic solvent such asmethanol, ethanol, butanol, benzene, toluene, N-methyl-2-pyrrolidone,N,N-dimethylacetamide or γ-butyrolactone or in water to make a solution,with which the surface of the substrate is coated by spin coating or thelike, followed by drying at 70 to 400° C. to from the film. Theorganozirconium compound may preferably have a film thickness in therange of from 50 angstroms or more to 200 or less.

As the resin constituting the second coupler layer 23 in the presentembodiments, a resin containing no fluorine may be used, and variousresins may be used, as exemplified by polyimide type resins, siliconetype resins, acrylic resins, polycarbonate type resins, epoxy typeresins, polyamide type resins, polyester type resins and phenolic typeresins. In uses where heat resistance is required in element productionsteps or in use environment, polyimide type resins, polyquinoline typeresins or the like are preferred. As the resin containing no fluorine, aresin containing nitrogen is preferred.

Where a polyimide type resin containing no fluorine is used as the resinof the second coupler layer 23 used in First and Second Embodiments, itmay include, e.g., polyimide resin,poly(imide.isoindoloquinazolinedioneimide) resin, polyether-imide resin,polyamide-imide resin and polyester-imide resin. As the resin containingno fluorine that is used as the resin of the second coupler layer 23 inthe present embodiments, in place of a resin containing no fluorine atall, a resin may be selected in which the fluorine content issufficiently lower than the fluorine content of polyimide type resinscontaining fluorine. In such a case, the fluorine content may preferablybe a half or less of that in the optical waveguide formed of a polyimidetype resin containing fluorine. Stated specifically, the fluorinecontent may preferably be 10% by weight or less, and more preferably 2%by weight or less.

In First and Second Embodiments, the polyimide type resin containingfluorine that is used to form the lower clad layer 3, optical waveguide4, upper clad layer 5 and so forth may include polyimide resin havingfluorine, poly(imide.isoindoloquinazolinedioneimide) resin havingfluorine, polyether-imide resin having fluorine, polyamide-imide resinhaving fluorine, and polyester-imide resin having fluorine. When thepolyamide-imide resin is obtained, trimellitic anhydride chloride or thelike is used. A precursor solution of the polyimide type resin isobtained by the reaction of a tetracarboxylic dianhydride with a diaminein a polar solvent such as N-methyl-2-pyrrolidone,N,N-dimethylacetamide, γ-butyrolactone or dimethyl sulfoxide. Aprecursor solution of the polyimide type resin having fluorine may beproduced by the reaction of a tetracarboxylic dianhydride havingfluorine with a diamine. A precursor solution of the polyimide typeresin having fluorine may also be produced by the reaction of atetracarboxylic dianhydride with a diamine having fluorine. A precursorsolution of a polyimide type resin having no fluorine may be producedwhere either of the tetracarboxylic dianhydride and the diamine has nofluorine.

As examples of the tetracarboxylic dianhydride having fluorine, it mayinclude (trifluoromethyl)pyromellitic dianhydride,di(trifluoromethyl)pyromelliticdianhydride,di(heptafluoropropyl)pyromellitic dianhydride,pentafluoroethylpyromellitic dianhydride,bis{3,5-(trifluoromethyl)phenoxy}pyromellitic dianhydride,2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride,5,5′-bis(trifluoromethyl)-3,3′,4,4′-tetracarboxyphenyl dianhydride,2,2′,5,5′-tetrakis(trifluoromethyl)-3,3′,4,4′-tetracarb oxyphenyldianhydride, 5,5′-bis(trifluoromethyl)-3,3′,4,4′-tetracarboxydiphenylether dianhydride,5,5′-bis(trifluoromethyl)-3,3′,4,4′-tetracarboxybenzophenonedianhydride, bis{(trifluoromethyl)dicarboxyphenoxy}benzene dianhydride,bis{(trifluoromethyl)dicarboxyphenoxy}(trifluoromethyl) benzenedianhydride, bis(dicarboxyphenoxy)(trifluoromethyl)benzene dianhydride,bis(dicarboxyphenoxy)bis(trifluoromethyl)benzene dianhydride,bis(dicarboxyphenoxy)tetrakis(trifluoromethyl)benzene dianhydride,2,2-bis{(4-(3,4-dicarboxyphenoxy)phenyl}hexafluoropropane dianhydride,bis{(trifluoromethyl)dicarboxyphenoxy}biphenyl dianhydride,bis{(trifluoromethyl)dicarboxyphenoxy}bis(trifluoromethyl)biphenyldianhydride, bis{(trifluoromethyl)dicarboxyphenoxy}diphenyl etherdianhydride, bis(dicarboxyphenoxy)bis(trifluoromethyl)biphenyldianhydride, 1,4-bis(2-hydroxyhexafluoroisopropyl)benzenebis(trimellitic anhydride), and1,3-bis(2-hydroxyhexafluoroisopropyl)benzene bis(trimellitic anhydride).Two or more of these may be used in the form of a mixture.

As examples of the tetracarboxylic dianhydride having no fluorine, itmay include pyromellitic dianhydride, benzene-1,2,3,4-tetracarboxylicdianhydride, 3,3′,4,4′-diphenyltetracarboxylic dianhydride,2,2′,3,3′-diphenyltetracarboxylic dianhydride,2,3′,3′,4-diphenyltetracarboxylic dianhydride,p-terphenyl-3,4,3″,4″-tetracarboxylic dianhydride,m-terphenyl-3,4,3″,4″-tetracarboxylic dianhydride,1,2,5,6-naphthalenetetracarboxylic dianhydride,2,3,6,7-naphthalenetetracarboxylic dianhydride,1,2,4,5-naphthalenetetracarboxylic dianhydride,1,4,5,8-naphthalenetetracarboxylic dianhydride,2,6-dichloronaphthalene-1,4,5,8-tetracarboxylic dianhydride,2,7-dichloronaphthalene-1,4,5,8-tetracarboxylic dianhydride,2,3,6,7-tetrachloronaphthalene-1,4,5,8-tetracarboxylic dianhydride,2,3,5,6-pyridinetetracarboxylicdianhydride,3,4,5,9,10-perilenetetracarboxylic dianhydride,3,3′,4,4′-benzophenonetetracarboxylic dianhydride,2,2′,3,3′-benzophenonetetracarboxylic dianhydride,2,3,3′,4′-benzophenonetetracarboxylic dianhydride, 3,3′,4,4′-biphenylether tetracarboxylic dianhydride, 4,4′-sulfonyldiphthalic dianhydride,3,3,4,4′-tetraphenylsilane tetracarboxylic dianhydride,3,3,4,4′-diphenyl ether tetracarboxylic dianhydride,1,3-bis(3,4-dicarboxyphenyl)-1,1,3,3-tetramethyldisiloxane dianhydride,1-(2,3-dicarboxyphenyl)-3-(3,4-dicarboxyphenyl)-1,1,3,3-tetramethyldisiloxanedianhydride, 2,2-bis(3,4-dicarboxyphenyl)propane dianhydride,2,2-bis(2,3-dicarboxyphenyl)propane dianhydride,1,1-bis(2,3-dicarboxyphenyl)ethane dianhydride,1,1-bis(3,4-dicarboxyphenyl)ethane dianhydride,bis(2,3-dicarboxyphenyl)methane dianhydride,bis(3,4-dicarboxyphenyl)methane dianhydride,bis(3,4-dicarboxyphenyl)sulfone dianhydride,phenanthrene-1,8,9,10-tetracarboxylic dianhydride,pyrazine-2,3,5,6-tetracarboxylic dianhydride,thiophene-2,3,4,5-tetracarboxylic dianhydride,bis(3,4-dicarboxyphenyl)dimethylsilane dianhydride,bis(3,4-dicarboxyphenyl)methylphenylsilane dianhydride,bis(3,4-dicarboxyphenyl)diphenylsilane dianhydride,1,4-bis(3,4-dicarboxyphenyldimethylsilyl)benzene dianhydride,1,3-bis(3,4-dicarboxyphenyl)-1,1,3,3-tetramethyldicyclo hexanedianhydride, p-phenylbis(trimellitic monoester anhydride), ethyleneglycol bis(trimellitic anhydride), propanediol bis(trimelliticanhydride), butanediol bis(trimellitic anhydride), pentanediolbis(trimellitic anhydride), hexanediol bis(trimellitic anhydride),octanediol bis(trimellitic anhydride), decanediol bis(trimelliticanhydride), ethylenetetracarboxylic dianhydride,1,2,3,4-butanetetracarboxylic dianhydride,decahydronaphthalene-1,4,5,8-tetracarboxylic dianhydride,4,8-dimethyl-1,2,3,5,6,7-hexahydronaphthalene-1,2,5,6-tetracarboxylicdianhydride, cyclopentane-1,2,3,4-tetracarboxylic dianhydride,pyrrolidine-2,3,4,5-tetracarboxylic dianhydride,1,2,3,4-cyclobutanetetracarboxylic dianhydride,bis(exo-bicyclo[2,2,1]heptane-2,3-dicarboxylic anhydride), sulfonebicyclo-(2,2,2)-octo(7)-ene-2,3,5,6-tetracarboxylic dianhydride,4,4′bis(3,4-dicarboxyphenoxy)diphenyl sulfide dianhydride,5-(2,5-dioxotetrahydrofuryl)-3-methyl-3-cyclohexene-1,2-dicarboxylicdianhydride, and tetrahydrofuran-2,3,4,5-tetracarboxylic dianhydride.Two or more of these may be used in the form of a mixture.

As examples of the diamine having fluorine, it may include4-(1H,1H,11H-eicosafluoroundecanoxy)-1,3-diaminobenzene,4-(1H,1H-perfluoro-1-butanoxy)-1,3-diaminobenzene,4-(1H,1H-perfluoro-1-heptanoxy)-1,3-diaminobenzene,4-(1H,1H-perfluoro-1-octanoxy)-1,3-diaminobenzene,4-pentafluoropheoxy-1,3-diaminobenzene,4-(2,3,5,6-tetrafluorophenoxy)-1,3-diaminobenzene,4-(4-fluorophenoxy)-1,3-diaminobenzene,4-(1H,1H,2H,2H-perfluoro-1-hexanoxy)-1,3-diaminobenzene,4-(1H,1H,2H,2H-perfluoro-1-dodecanoxy)-1,3-diaminobenzene,(2,5-)diaminobenzotrifluoride, bis(trifluoromethyl)phenylenediamine,diaminotetra(trifluoromethyl)benzene, diamino(pentafluoroethyl)benzene,2,5-diamino(perfluorohexyl)benzene, 2,5-diamino(perfluorobutyl)benzene,1,4-bis(4-aminophenyl)benzene,p-bis(4-amino-2-trifluormethylphenoxy)benzene,bis(aminophenoxy)bis(trifluoromethyl)benzene,bis(aminophenoxy)tetrakis(trifluoromethyl)benzene,bis{2-[(aminophenoxy)phenyl]hexafluoroisopropyl}benzene,2,2′-bis(trifluoromethyl)-4,4′-diaminobiphenyl,3,3′-bis(trifluoromethyl)-4,4′-diaminobiphenyl, octafluorobenzidine,bis{(trifluoromethyl)aminophenoxy}biphenyl,4,4′-bis(4-amino-2-trifluormethylphenoxy)biphenyl,4,4′-bis(4-amino-3-trifluormethylphenoxy)biphenyl,1,4-bis(anilino)ocafluorobutane, 1,5-bis(anilino)decafluoropentane,1,7-bis(anilino)tetradecafluoroheptane,3,3′-difluoro-4,4′-diaminodiphenyl ether,3,3′,5,5′-tetrafluoro-4,4′-diaminodiphenyl ether,2,2-bis(trifluoromethyl)-4,4′-diaminodiphenyl ether,3,3-bis(trifluoromethyl)-4,4′-diaminodiphenyl ether,3,3′,5,5′-tetrakis(trifluoromethyl)-4,4′-diaminodiphenyl ether,3,3′-difluoro-4,4′-diaminodiphenylmethane,3,3′-di(trifluomethyl)-4,4′-diaminodiphenylmethane,3,3′,5,5′-tetrafluoro-4,4′-diaminodiphenylmethane,3,3′,5,5′-tetrakis(trifluoromethyl)-4,4′-diaminodiphenylmethane,3,3′-difluoro-4,4′-diaminodiphenylpropane,3,3′,5,5′-tetrafluoro-4,4′-diaminodiphenylpropane,3,3′-bis(trifluoromethyl)-4,4′-diaminodiphenylpropane,3,3′,5,5′-tetrakis(trifluoromethyl)-4,4′-diaminodiphenylpropane,3,3′-difluoro-4,4′-diaminodiphenylsulfone,3,3′,5,5′-tetrafluoro-4,4′-diaminodiphenylsulfone,3,3′-bis(trifluoromethyl)-4,4′-diaminodiphenylsulfone,3,3′,5,5′-tetrakis(trifluoromethyl)-4,4′-diaminodiphenylsulfone,4,4′-bis(4-amino-2-trifluoromethylphenoxy)diphenylsulfone,4,4′-bis(3-amino-5-trifluoromethylphenoxy)diphenylsulfone,3,3′-difluoro-4,4′-diaminodiphenyl sulfide,3,3′,5,5′-tetrafluoro-4,4′-diaminodiphenyl sulfide,3,3′-bis(trifluoromethyl)-4,4′-diaminodiphenyl sulfide,3,3′,5,5′-tetrakis(trifluoromethyl)-4,4′-diaminodiphenyl sulfide,3,3′-difluoro-4,4′-diaminobenzophenone,3,3′,5,5′-tetrafluoro-4,4′-diaminobenzophenone,3,3′-bis(trifluoromethyl)-4,4′-diaminobenzophenone,3,3′,5,5′-tetrakis(trifluoromethyl)-4,4′-diaminobenzophenone,4,4′-diamino-p-terphenyl,3,3′-dimethyl-4,4′-diaminodiphenylhexafluoropropane,3,3′-dimethoxy-4,4′-diaminodiphenylhexafluoropropane,3,3′-diethoxy-4,4′-diaminodiphenylhexafluoropropane,3,3′-difluoro-4,4′-diaminodiphenylhexafluoropropane,3,3′-dichloro-4,4′-diaminodiphenylhexafluoropropane,3,3′-dibromo-4,4′-diaminodiphenylhexafluoropropane,3,3′,5,5′-tetamethyl-4,4′-diaminodiphenylhexafluoropropane,3,3′,5,5′-tetamethoxy-4,4′-diaminodiphenylhexafluoropropane,3,3′,5,5′-tetaethoxy-4,4′-diaminodiphenylhexafluoropropane,3,3′,5,5′-tetrafluoro-4,4′-diaminodiphenylhexafluoropropane,3,3′,5,5′-tetachloro-4,4′-diaminodiphenylhexafluoropropane,3,3′,5,5′-tetabromo-4,4′-diaminodiphenylhexafluoropropane,3,3′,5,5′-tetakis(trifluoromethyl)-4,4′-diaminodiphenylhexafluoropropane,3,3′-bis(trifluoromethyl)-4,4′-diaminodiphenylhexafluoropropane,2,2-bis(4-aminophenyl)hexafluoropropane,1,3-bis(anilino)hexafluoropropane,2,2-bis{4-(4-aminophenoxy)phenyl}hexafluoropropane,2,2-bis{4-(3-aminophenoxy)phenyl}hexafluoropropane,2,2-bis{4-(2-aminophenoxy)phenyl}hexafluoropropane,2,2-bis{4-(4-aminophenoxy)-3,5-dimethylphenyl}hexafluoropropane,2,2-bis{4-(4-aminophenoxy)-3,5-ditrifluoromethylphenyl}hexafluoropropane,2,2-bis{4-(4-amino-3-trifluoromethylphenoxy)phenyl}hexafluoropropane,bis[{(trifluoromethylaminophenoxy}phenyl]hexafluoropropane,1,3-diamino-5-(perfluorononenyloxy)benzene,1,3-diamino-4-methyl-5-(perfluorononenyloxy)benzene,1,3-diamino-4-methoxy-5-(perfluorononenyloxy)benzene,1,3-diamino-2,4,6-trifluoro-5-(perfluorononenyloxy)benzene,1,3-diamino-4-chloro-5-(perfluorononenyloxy)benzene,1,3-diamino-4-bromo-5-(perfluorononenyloxy)benzene,1,2-diamino-4-(perfluorononenyloxy)benzene,1,2-diamino-4-methyl-5-(perfluorononenyloxy)benzene,1,2-diamino-4-methoxy-5-(perfluorononenyloxy)benzene,1,2-diamino-3,4,6-trifluoro-5-(perfluorononenyloxy)benzene,1,2-diamino-4-chloro-5-(perfluorononenyloxy)benzene,1,2-diamino-4-bromo-5-(perfluorononenyloxy)benzene,1,4-diamino-3-(perfluorononenyloxy)benzene,1,4-diamino-2-methyl-5-(perfluorononenyloxy)benzene,1,4-diamino-2-methoxy-5-(perfluorononenyloxy)benzene,1,4-diamino-2,3,6-trifluoro-5-(perfluorononenyloxy)benzene,1,4-diamino-2-chloro-5-(perfluorononenyloxy)benzene,1,4-diamino-2-bromo-5-(perfluorononenyloxy)benzene,1,3-diamino-5-(perfluorohexenyloxy)benzene,1,3-diamino-4-methyl-5-(perfluorohexenyloxy)benzene,1,3-diamino-4-methoxy-5-(perfluorohexenyloxy)benzene,1,3-diamino-2,4,6-trifluoro-5-(perfluorohexenyloxy)benzene,1,3-diamino-4-chloro-5-(perfluorohexenyloxy)benzene,1,3-diamino-4-bromo-5-(perfluorohexenyloxy)benzene,1,2-diamino-4-(perfluorohexenyloxy)benzene,1,2-diamino-4-methyl-5-(perfluorohexenyloxy)benzene,1,2-diamino-4-methoxy-5-(perfluorohexenyloxy)benzene,1,2-diamino-3,4,6-trifluoro-5-(perfluorohexenyloxy)benzene,1,2-diamino-4-chloro-5-(perfluorohexenyloxy)benzene,1,2-diamino-4-bromo-5-(perfluorohexenyloxy)benzene,1,4-diamino-3-(perfluorohexenyloxy)benzene,1,4-diamino-2-methyl-5-(perfluorohexenyloxy)benzene,1,4-diamino-2-methoxy-5-(perfluorohexenyloxy)benzene,1,4-diamino-2,3,6-trifluoro-5-(perfluorohexenyloxy)benzene,1,4-diamino-2-chloro-5-(perfluorohexenyloxy)benzene, and1,4-diamino-2-bromo-5-(perfluorohexenyloxy)benzene. Two or more of thesemay be used in the form of a mixture.

As examples of the diamine having no fluorine, it may includep-phenylenediamine, m-phenylenediamine, 2,6-diaminopyridine,1,5-diaminonaphthalene, 2,6-diaminonaphthalene, benzidine,3,3′-dimethylbenzidine, 3,3′-dimethoxybenzidine,3,3′-diaminobenzophenone, 3,3′-dimethyl-4,41-diaminobenzophenone,3,3′-dimethoxy-4,4′-diaminobenzophenone,3,3′-diethoxy-4,4′-diaminobenzophenone,3,3′-dichloro-4,4′-diaminobenzophenone,3,3′-dibromo-4,4′-diaminobenzophenone,3,3′5,5′-tetramethyl-4,4′-diaminobenzophenone,3,3′5,5′-tetramethoxy-4,4′-diaminobenzophenone,3,3′5,5′-tetraethoxy-4,4′-diaminobenzophenone,3,3′5,5′-tetrachloro-4,4′-diaminobenzophenone,3,3′5,5′-tetrabromo-4,4′-diaminobenzophenone, 4,4′-diaminodiphenylether, 3,4′-diaminodiphenyl ether, 3,3′-diaminodiphenyl ether,3,3′-dimethyl-4,4′-diaminodiphenyl ether,3,3′-diisopropyl-4,4′-diaminodiphenyl ether,3,3′-dimethoxy-4,4′-diaminodiphenyl ether,3,3′-diethoxy-4,4′-diaminodiphenyl ether,3,3′-dichloro-4,4′-diaminodiphenyl ether,3,3′-dibromo-4,4′-diaminodiphenyl ether,3,3′,5,5′-tetramethyl-4,4′-diaminodiphenyl ether,3,3′,5,5′-tetraethyl-4,4′-diaminodiphenyl ether,3,3′,5,5′-tetramethoxy-4,4′-diaminodiphenyl ether,3,3′,5,5′-tetraethoxy-4,4′-diaminodiphenyl ether,3,3′,5,5′-tetrachloro-4,4′-diaminodiphenyl ether,3,3′,5,5′-tetrabromo-4,4′-diaminodiphenyl ether,3,3′-diisopropyl-5,5′-dimethyl-4,4′-diaminodiphenyl ether,3,3′-diisopropyl-5,5′-diethyl-4,4′-diaminodiphenyl ether,4,4′-diaminodiphenylmethane, 3,3′-diaminodiphenylmethane,3,3′-dimethyl-4,4′-diaminodiphenylmethane,3,3′-diethyl-4,4′-diaminodiphenylmethane,3,3′-dimethoxy-4,4′-diaminodiphenylmethane,3,3′-diethoxy-4,4′-diaminodiphenylmethane,3,3′-dichloro-4,4′-diaminodiphenylmethane,3,3′-dibromo-4,4′-diaminodiphenylmethane,3,3′,5,5′-tetramethyl-4,4′-diaminodiphenylmethane,3,3′,5,5′-tetraisopropyl-4,4′-diaminodiphenylmethane,3,3′,5,5′-tetramethoxy-4,4′-diaminodiphenylmethane,3,3′,5,5′-tetraethoxy-4,4′-diaminodiphenylmethane,3,3′,5,5′-tetrachloro-4,4′-diaminodiphenylmethane,3,3′,5,5′-tetrabromo-4,4′-diaminodiphenylmethane,3,3′,5,5′-tetraisopropyl-4,4′-diaminodiphenylmethane,3,3′-diisopropyl-5,5′-dimethyl-4,4′-diaminodiphenylmethane,3,3′-diisopropyl-5,5′-diethyl-4,4′-diaminodiphenylmethane,4,4′-diaminodiphenylpropane, 3,3′-diaminodiphenylpropane,3,3′-dimethyl-4,4′-diaminodiphenylpropane,3,3′-dimethoxy-4,4′-diaminodiphenylpropane,3,3′-diethoxy-4,4′-diaminodiphenylpropane,3,3′-dichloro-4,4′-diaminodiphenylpropane,3,3′-dibromo-4,4′-diaminodiphenylpropane,3,3′,5,5′-tetramethyl-4,4′-diaminodiphenylpropane,3,3′,5,5′-tetramethoxy-4,4′-diaminodiphenylpropane,3,3′,5,5′-tetraethoxy-4,4′-diaminodiphenylpropane,3,3′,5,5′-tetrachloro-4,4′-diaminodiphenylpropane,3,3′,5,5′-tetrabromo-4,4′-diaminodiphenylpropane,3,3′-diisopropyl-5,5′-dimethyl-4,4′-diaminodiphenylpropane,3,3′-diisopropyl-5,5′-diethyl-4,4′-diaminodiphenylpropane,4,4′-diaminodiphenylsulfone, 3,3′-diaminodiphenylsulfone,3,3′-dimethyl-4,4′-diaminodiphenylsulfone,3,3′-dimethoxy-4,4′-diaminodiphenylsulfone,3,3′-diethoxy-4,4′-diaminodiphenylsulfone,3,3′-dichloro-4,4′-diaminodiphenylsulfone,3,3′-dibromo-4,4′-diaminodiphenylsulfone,3,3′,5,5′-tetramethyl-4,4′-diaminodiphenylsulfone,3,3′,5,5′-tetramethoxy-4,4′-diaminodiphenylsulfone,3,3′,5,5′-tetraethoxy-4,4′-diaminodiphenylsulfone,3,3′,5,5′-tetrachloro-4,4′-diaminodiphenylsulfone,3,3′,5,5′-tetrabromo-4,4′-diaminodiphenylsulfone,3,3′-diisopropyl-5,5′-dimethyl-4,4′-diaminodiphenylsulfone,3,3′-diisopropyl-5,5′-diethyl-4,4′-diaminodiphenylsulfone,4,4′-diaminodiphenyl sulfide, 3,3′-diaminodiphenyl sulfide,3,3′-dimethyl-4,4′-diaminodiphenyl sulfide,3,3′-dimethoxy-4,4′-diaminodiphenyl sulfide,3,3′-diethoxy-4,4′-diaminodiphenyl sulfide,3,3′-dichloro-4,4′-diaminodiphenyl sulfide,3,3′-dibromo-4,4′-diaminodiphenyl sulfide,3,3′,5,5′-tetramethyl-4,4′-diaminodiphenyl sulfide,3,3′,5,5′-tetramethoxy-4,4′-diaminodiphenyl sulfide,3,3′,5,5′-tetraethoxy-4,4′-diaminodiphenyl sulfide,3,3′,5,5′-tetrachloro-4,4′-diaminodiphenyl sulfide,3,3′,5,5′-tetrabromo-4,4′-diaminodiphenyl sulfide,1,4-bis(4-aminophenoxy)benzene, 1,3-bis(4-aminophenoxy)benzene,2,2-bis(4-aminophenoxyphenyl)propane, bis(4-aminophenoxyphenyl)sulfone,bis(4-aminophenoxyphenyl)sulfide, bis(4-aminophenoxyphenyl)biphenyl,4,4′-diaminodiphenyl ether-3-sulfonamide, 3,4′-diaminodiphenylether-4-sulfonamide, 3,4′-diaminodiphenyl ether-3′-sulfonamide,3,3′-diaminodiphenyl ether-4-sulfonamide,4,4′-diaminodiphenylmethane-3-sulfonamide,3,4′-diaminodiphenylmethane-4-sulfonamide,3,4′-diaminodiphenylmethane-3′-sulfonamide,3,3′-diaminodiphenylmethane-4-sulfonamide,4,4′-diaminodiphenylsulfone-3-sulfonamide,3,4′-diaminodiphenylsulfone-4-sulfonamide,3,4′-diaminodiphenylsulfone-3′-sulfonamide,3,3′-diaminodiphenylsulfone-4-sulfonamide, 4,4′-diaminodiphenylsulfide-3-sulfonamide, 3,4′-diaminodiphenyl sulfide-4-sulfonamide,3,3′-diaminodiphenyl sulfide-4-sulfonamide, 3,4′-diaminodiphenylsulfide-3′-sulfonamide, 1,4-diaminobenzene-2-sulfonamide,4,4′-diaminodiphenyl ether-3-carbonamide, 3,4′-diaminodiphenylether-4-carbonamide, 3,4′-diaminodiphenyl ether-3′-carbonamide,3,3′-diaminodiphenyl ether-4-carbonamide, 3,3′-diaminodiphenylether-4-carbonamide, 4,4′-diaminodiphenylmethane-3-carbonamide,3,4′-diaminodiphenylmethane-4-carbonamide,3,4′-diaminodiphenylmethane-3′-carbonamide,3,3′-diaminodiphenylmethane-4-carbonamide,4,4′-diaminodiphenylsulfone-3-carbonamide,3,4′-diaminodiphenylsulfone-4-carbonamide,3,4′-diaminodiphenylsulfone-3′-carbonamide,3,3′-diaminodiphenylsulfone-4-carbonamide, 4,4′-diaminodiphenylsulfide-3-carbonamide, 3,4′-diaminodiphenyl sulfide-4-carbonamide,3,3′-diaminodiphenyl sulfide-4-carbonamide, 3,4′-diaminodiphenylsulfide-3′-carbonamide, 1,4-diaminobenzene-2-carbonamide,4-aminophenyl-3-aminobenzoic acid, 2,2-bis(4-aminophenyl)propane,bis(4-aminophenyl)diethylsilane, bis(4-aminophenyl)diphenylsilane,bis(4-aminophenyl)ethylphosphine oxide, bis(4-aminophenyl)-N-butylamine,bis(4-aminophenyl)-N-methylamine, N-(3-aminophenyl)-4-aminobenzamide,2,4-bis(β-amino-t-butyl)toluene, bis(p-β-amino-t-butylphenyl) ether,bis(p-β-amino-γ-aminopentyl) benzene,bis-p-(1,1-dimethyl-5-aminopentyl)benzene, hexamethylenediamine,heptamethylenediamine, octamethylenediamine, nonamethylenediamine,decamethylenediamine, tetramethylenediamine, propylenediamine,3-methylheptamethylenediamine, 4,4′-dimethylheptamethylenediamine,2,11-diaminododecane, 1,2-bis-(3-aminopropoxy)ethane,2,2-dimethylpropylenediamine, 3-methoxy-hexamethylenediamine,2,5-dimethylhexamethylenediamine, 2,5-dimethylheptamethylenediamine,5-methylnonamethylenediamine, 2,17-diaminoicosadecane,1,4-diaminocyclohexane, 1,10-diamino-1,10-dimethyldecane, and1,12-diaminooctadecane. Two or more of these may be used in the form ofa mixture.

As a part of the diamine, a silicon diamine may be used. The silicondiamine includes 1,3-bis(3-aminopropyl)-1,1,1-tetraphenyldisloxane,1,3-bis(3-aminopropyl)-1,1,1-tetramethyldisloxane, and1,3-bis(4-aminobutyl)-1,1,1-tetramethyldisloxane. In the case when thesilicon diamine is used, any of these may preferably be used in anamount of from 0.1 to 10 mol % based on the total weight of the diamine.The above tetracarboxylic dianhydride and the diamine may each be usedin combination of two or more. As the precursor solutions of thepolyimide type resins, those having sensitivity may also be used.

In First and Second Embodiments, the second coupler layer 23 maypreferably have a thickness of 10 μm or less. If it has a thickness ofmore than 10 μm, the whole resin films of the second coupler layer 23and polyimide type resin films having fluorine (layers of from the lowerclad layer 3 up to the protective layer 9) have so large a thickness asto cause awarpagedue to a stress coming from a difference in coefficientof expansion between the films and the substrate. The uniformity ofthickness of the whole resin films may also be achieved with difficulty.In particular, the second coupler layer 23 may more have a thickness of1.0 μm or less. The thickness of the second coupler layer 23 mustoptimally be selected in accordance with the structure of the opticalwaveguide formed thereon which is produced using the polyimide typeresin films having fluorine (layers of from the lower clad layer 3 up tothe protective layer 9). More specifically, where an optical-waveguidemulti-layer member is formed in which the top of the second couplerlayer 23 is directly provided with a core (the optical waveguide 4) orwhere an optical-waveguide multi-layer member is formed which is so madeup that the second coupler layer 23 and the optical waveguide 4 stand inproximity (i.e., the clad layer 3 positioned between the second couplerlayer 23 and the optical waveguide 4 has a small thickness), the secondcoupler layer 23 can be a factor of great light loss. Accordingly, thesecond coupler layer 23 may preferably be formed in a small thickness.Specific thickness should be determined taking account of the refractiveindices and respective heights, widths and so forth of the substrate 1,the second coupler layer 23 formed of polyimide type resin having nofluorine, the clad layers 3 and 5 formed using polyimide type resinhaving fluorine and the optical waveguide 4. In general, taking accountof the matching with optical fibers which are transmission paths, and inorder to well reduce any loss for the light being propagated within thatwaveguide 4 because the optical waveguide 4 formed of polyimide typeresin having fluorine is formed in a size of about 10 μm in many cases,the second coupler layer 23 may preferably be formed in a thickness of1/10 or less of the size of the optical waveguide 4. In the case of theabove example, it may more preferably be formed in a thickness of 1.0 μmor less, and still more preferably 0.5 μm or less.

As the polyimide precursor solution used to form the second couplerlayer 23 in First and Second Embodiments, a solution prepared in thefollowing way may also be used. That is, it is a solution obtained bydissolving 35.33 g of 4,4′-diaminodiphenyl ether and 4.77 g of4,4′-diaminodiphenyl ether-3-carbonamide in 28.3 g ofN-methyl-2-pyrrolidone, and thereafter adding 31.69 g of3,3′,4,4′-benzophenonetetracarboxylic dianhydride and 21.44 g ofpyrotrimellitic dianhydride, followed by stirring at room temperaturefor 6 hours.

As the precursor solution used to form in First and Second Embodimentsthe polyimide layers having fluorine which constitute the layers of fromthe lower clad layer 3 up to the protective layer 9, a solution preparedin the following way may be used. That is, it is a solution obtained bydissolving 1.47 g of 2,2-bis(4-aminophenyl)hexafluoropropane in 450 g ofN,N-dimethylacetamide, and thereafter adding 28.53 g of2,2′-bis(3.4-dicarboxyphenyl)hexafluoropropane dianhydride, followed bystirring at room temperature for 20 hours.

In First and Second Embodiments, as the second coupler layer 23, apolyimide silicone resin may also be used which has Si atoms in themolecular structure and has a strong self-adherence to silicon or SiO₂.An acrylic resin having no fluorine or a polycarbonate type resin havingno fluorine may also be used as the resin of the second coupler layer23.

As the polyimide silicone resin, usable is a polymerization product of abenzophenonetetracarboxylic dianhydride (BTDA), methylenedianiline (MDA)and bis-γ-aminopropyltetramethyldisiloxane (GAPD), which is representedby the structural formula:

As the resin constituting the clad layers 3 and 5, the followingfluorinated polyimide A may be used. The fluorinated polyimide A is apolymerization product of a2,2′-bis(trifluoromethyl)-4,4′-diaminobiphenyl (TFDB) and2,2′-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA), whichis represented by the structural formula:

Also, as the resin constituting the optical waveguide 4, the followingfluorinated polyimide resin B may be used. The fluorinated polyimideresin B is a polymerization product of TFDB, 6FDA and pyromelliticdianhydride (PMDA), which is represented by the structural formula:

The 6FDA and the TFDB may be used in a proportion (i.e., proportion of mto n) of 4:1 so that the refractive index of the optical waveguide 4 islarger by about 0.3% than the refractive index of the clad layers 3 and5.

As having been described above, the present invention can provide anoptical element production process that can remove films in recesseswith ease in the step of producing optical elements making use of asubstrate having recesses.

1. An optical element comprising a substrate, and disposed on the substrate an optical-waveguide structure layer made of a resin, wherein: said optical-waveguide structure layer comprises an optical waveguide and a clad layer, an organozirconium compound layer is provided as a coupler layer between said substrate and said optical-waveguide structure layer, said organozirconium compound layer has, in a region beneath said optical waveguide, a film thickness distribution in the range of from a minimum film thickness of 50 angstroms or more to a maximum film thickness of 150 angstroms or less, said optical-waveguide structure layer is disposed on a first region of said substrate; and a recess is formed in a second region of said substrate, where said optical-waveguide structure layer is not disposed on said substrate.
 2. The optical element according to claim 1, wherein said optical-waveguide structure layer is formed of a resin material containing fluorine, and a resin layer containing no fluorine is disposed between said coupler layer and said optical-waveguide structure layer.
 3. The optical element according to claim 1 wherein said substrate has a registration mark.
 4. The optical element according to claim 1, wherein said recess is for mounting an optical fiber.
 5. The optical element according to claim 1, wherein said coupler layer is a first coupler layer, and wherein the optical element includes a second coupler layer, wherein the second coupler layer contains no organometallic compound.
 6. The optical element according to claim 5, wherein said second coupler layer is positioned between the first coupler layer and the optical-waveguide structure layer.
 7. The optical element according to claim 5, wherein said second coupler layer is a polyimide resin film containing no fluorine.
 8. An optical element comprising a substrate; an optical waveguide made of a resin, mounted on the substrate at its some part; a groove provided in a region of a top surface of the substrate in which region the optical waveguide is not mounted; and an electrode provided in a region of the top surface of the substrate in which region the optical waveguide is not mounted, wherein an organozirconium compound layer is disposed as a coupler layer between said substrate and said optical waveguide, said organozirconium compound layer has, in a region beneath said optical waveguide, a film thickness distribution in the range of from a minimum film thickness of 50 angstroms or more to a maximum film thickness of 150 angstroms or less, and a recess formed together with said groove in the step of forming said groove, is disposed around said electrode.
 9. The optical element according to claim 8, wherein said optical-waveguide structure layer is formed of a resin material containing fluorine, and a resin layer containing no fluorine is disposed between said coupler layer and said optical-waveguide structure layer.
 10. The optical element according to claim 8, wherein said recess is for mounting an optical fiber. 